Emergency light circuit for mercury vapor lamps

ABSTRACT

An auxiliary or emergency lighting system for use with electric discharge lamps, and more particularly mercury vapor lamps. Means are provided for detecting the loss of energy or illumination in the primary discharge lamps and responding thereto to turn on an emergency lamp. In one embodiment, the emergency lamp may be selectively supplied with electricity from either the primary power source or from a battery, depending upon whether the electrical discharge lamps are momentarily or permanently deprived of energy. The battery for the emergency lamp is charged by a charging circuit connected to the primary power source and operative during normal operation of the electrical discharge lamp. A second embodiment uses a light-detecting device for triggering the emergency lamp into operation and includes means for providing both a fast charge and a trickle charge to the battery, depending upon the charge state of the battery.

United States Patent Appleton EMERGENCY LIGHT CIRCUIT FOR MERCURY VAPORLAMPS Arthur I. Appleton, 1713 West Wellington Ave., Chicago, 111. 60613Filed: Nov. 10, 1969 Appl. No.: 875,113

Inventor:

References Cited UNITED STATES PATENTS 10/1963 Bagno ..307/66 Gershen250/206 X McNamara, .lr. ..3 15/91 [451 Jan. 18, 1972 PrimaryExaminer-Raymond F. l-lossfeld AttorneyWolfe, Hubbard, Leydig, Voit &Osann, Ltd.

[57] ABSTRACT An auxiliary or emergency lighting system for use withelectric discharge lamps, and more particularly mercury vapor lamps.Means are provided for detecting the loss of energy or illumination inthe primary discharge lamps and responding thereto to turn on anemergency lamp. in one embodiment, the emergency lamp may be selectivelysupplied with electricity from either the primary power source or from abattery, depending upon whether the electrical discharge lamps aremomentarily or permanently deprived of energy. The battery for theemergency lamp is charged by a charging circuit conn ected to theprimary power source and operative during normal operation of theelectrical discharge lamp. A second embodiment uses a light-detectingdevice for triggering the emergency lamp into operation and includesmeans for providing both a fast charge and a trickle charge to thebattery, depend ing upon the charge state of the battery.

13 Claims, 2 Drawing Figures EMERGENCY LIGHT CIRCUIT FOR MERCURY VAPORLAMPS BACKGROUND Electrical gaseous discharge lamps emit light bysustaining an arc through a gas atmosphere in a bulb. Mercury vapor is acommonly used gas for this purpose; consequently, mercury vapor lampswill be used as an illustrative example of the primary illuminationsource in the subsequent discussion of the invention. The voltagerequired to sustain the arc in the lamp during ordinary operation issubstantially less than that required to strike the arc initially. Thusthe power to the mercury lamp is first channeled through a ballast"which serves to supply the lamp with a high initial voltage to strikethe arc and a lower sustaining (or operating) voltage after the arc ismade. As the lamp continues in operation, it warms to a temperatureconsiderably higher than that of the air surrounding it. Eventually itwill reach a state of thermal equilibrium. Should the arc for any reasonbe extinguished after the lamp has reached its operating temperature, asignificant problem will arise. The starting voltage required for a hotlamp is significantly higher than that required for a cold lamp, thevoltage required being a function of temperature. Immediately after thearc is extinguished, the starting voltage required may be many times thecold starting voltage. It then decreases with the passage of time as thelamp cools. The ballast" or starting circuit for electric dischargelamps is very often incapable of supplying this unusually high startingvoltage. Therefore, until the lamp cools considerably the ballast willbe unable to restrike the are, this cooling process typically requiringbetween and l5 minutes. During the cooling period the light will becompletely out even though the line voltage may have been onlymomentarily interrupted,

Emergency lighting systems for providing illumination during a momentarydrop in line voltage to a mercury vapor lamp have been proposed in thepast. For instance, one prior circuit utilized an emergency lampconnected in parallel with the primary electric discharge lamp. When theprimary lamp was extinguished by a momentary drop is in the linevoltage, the emergency lamp provided an alternate path for the currentand was illuminated. The difficulty with this arrangement lies in thefact that no emergency lighting is provided when the line current isinterrupted for an appreciable period.

DESCRIPTION OF THE INVENTION The present invention overcomes theproblems arising in prior emergency lighting systems for electricaldischarge lamps in a manner heretofore untaught in the art.

It is an object of the present invention to provide an emergencylighting system for use with electric discharge lamps by means of whichemergency illumination is provided whenever the power for the dischargelamps is interrupted, whether the interruption be momentary orprolonged.

It is another object of the present invention to provide an emergencylighting system which derives its power from the normal power source orline voltage when it is available, but which, when the line voltage isnot available, is supplied by its own self-contained source of power.

It is a further object of the present invention to provide means fordetecting an interruption in the illumination of electric dischargelamps whether that interruption be from a fluctuation in the powersupply to said lamps or from an inherent difficulty arising in the lampsthemselves.

A still further object of the present invention is the provision of anemergency lighting system which is adaptable to a wide variety ofconfigurations of electric discharge lamps and power sources for thesame. It is a related object of the invention that the system be simple,inexpensive and capable of operation with only a minimum amountofelectrical power.

Still another object of the present invention is the provision of anemergency lighting system which is virtually maintenance-free whilebeing capable of many consecutive operations.

Other objects and advantages of the present invention will becomeapparent upon reading the attached detailed description and uponreference to the drawings in which:

FIG. 1 is a diagram of an emergency lighting system constructed inaccordance with the present invention; and

FIG. 2 is a diagram of an alternative embodiment of the presentinvention.

While the invention has been described in connection with a preferredembodiment, we do not intend to limit the invention to the form setforth, but, on the contrary, we intend to cover such alternatives,modifications and equivalents as may be included within the spirit andscope of the invention.

Turning then to FIG. 1, there is shown a primary or main lightingcircuit including a pair of electrical discharge lamps 10, 11 connectedin series, with their cases grounded via a line 12. A ballast circuit 15is provided for the purpose of supplying the lamps 10, 11 with theirrequired starting and operating voltages. The ballast circuit istypically includes a transformer 16 consisting of primary and secondarywindings 17, 18. It is also common practice to use an autotransformerfor this purpose in place of the conventional transformer 16. Theprimary 17 of the transformer 16 is connected to an alternating currentpower source (not shown) via the lines 20, 21, one of which has a switch22 thereacross for controlling the application of line voltage to thecircuit. One side of the winding 18 of the transformer 16 is connectedto the lamp 10 via a line. 25 having an R-C dropping circuit 26 disposedtherein. The other side of the coil 18 is connected to the lamp 11through the energization coil 27 of a relay 28 and through a heatingresistor 29. The lamps l0, 1 1, R-C dropping circuit 26, coil 27 andheating resistor 29 form a series loop with the secondary winding 18 ofthe transformer 16.

The electrical discharge lamps 10, 11 are of the type having a metalvapor; such as mercury vapor, contained therein for sustaining anelectrical are between a pair of electrodes also contained therein. Thevoltage required to sustain the arc during ordinary operation isconsiderably less than that required to strike the are initially. Thestarting voltage depends to a great extent on the temperature of thelamp. A heated lamp, such as one which has just been turned off afteroperating for a prolonged period, may require twice the startingpotential needed for a cold lamp. The ballast circuit 15 is designed toprovide a high starting voltage, but only sufficient to start a lamp atroom temperature, and a lower sustaining voltage after the arc is made.Since the current flowing through the lamps 10, 11 is effectively zerobefore the arc is struck and increases as the operating or sustainingvoltage decreases, a simple transformer such as that shown in 16 isadequate and conventionally used as a ballast.

A problem arises when the arc in the lamps l0, 1 1 is extinguished, thesolution for which forms the basis of this invention. Until the lamps10, l 1 cool down to near room temperature, the ballast circuit 15willbe incapable of providing a sufficiently high starting voltage torestrike the arc.

Therefore, in accordance with one aspect of the present invention, asecondary lighting circuit is provided to furnish emergency illuminationwhen, for any reason, the arc in the lamps 10, 11 is extinguished. Tothis end, an emergency lamp 40 is provided, which is selectivelyconnected via lines 41, 42 to power sources hereinafter described. Theemergency lamp 40 shown in FIG. 1 is intended to be an incandescent lampcapable of either AC or DC operation when supplied with a nominalvoltage of 12 volts; however, other lamps may serve equally well in thecircuit with only minor modifications.

For the purpose of providing an auxiliary power supply for the emergencylamp 40 in the absence of a line voltage on the lines 20, 21 a storagebattery 45 is furnished as a secondary power source. A battery-chargingcircuit is also provided, including a transformer 47, a bridge rectifier48 and a dropping impedance 49. A primary winding 51 of the transformer47 is connected via lines 53, 52 to the power input lines 20, 21,respectively, while the secondary winding 55 is connected across theinput terminals 56, 57 of the bridge rectifier 48.

The bridge 48 consists of four diodes 60-63 arranged to provide afull-wave rectified signal across a pair of output terminals 65, 66.

The transformer 47 has a plurality of contacts on its primary winding 51so that it is universally adaptable to a number of conventional linevoltages, such as those shown opposite the primary terminals. Since thestorage battery 45 is being charged through the dropping impedance 49,it is desirable to supply the input terminals 56, 57 of the bridge 48with a peak voltage somewhat higher than the nominal voltage of thebattery 45. For instance, if the battery 45 is fully chargeable to 12volts, the transformer 47 will typically be designed and connected tosupply a peak voltage of approximately 16 volts across its secondarywinding 55.

For the purpose of controlling the charging current to the battery 45and preventing an overcharge thereof, a pressure switch 75 is connectedbetween the battery 45 and its charging circuit. The storage battery 45may be of the nickel cadmium variety, in which case a sensing element 76of the pressure switch 75 will be inserted to sense the pressure createdby the emission of gases in the cells of the battery during its chargingprocess. As the battery 45 reaches its fully charged state, the pressuredetected by the sensor 76 triggers the switch 75 to its open position,as shown in FIG. 1. The use of such a protective device allows a moresubstantial charging current to be applied to the storage battery 45without any danger of damaging the cells. Also provided is a means forlimiting the time during which the storage battery 45 may be dischargedto supply a load. This function is accomplished in the present case by athermal time delay switch 79 which is thermally coupled to the heatingresistor 29 via a heat sink 80. The heating resistor 29 is chosen forlow resistance and high wattage so that its temperature risesconsiderably, typically to 200 F. or more, when current flows in theprimary lighting circuit. The thermal time switch 79 will close as thetemperature of the resistor 29 passes a fixed threshold. Because of aninherent hysteresis effect in the thermal time switch 79, thetemperature created by the heating resistor 29 will have to dropsomewhat below this closing threshold temperature before the switch 79will again open. Typical of thermal time switches meeting the aboverequirements is one designated Therm-O- Disk, type 60T22, a single-pole,single-throw switch which closes at 190 F. and opens at 150 F.

In accordance with another aspect of the present invention, thesecondary lighting circuit is selectively connected to be supplied bythe primary power source in the instance where power to the lamps l0, 11is only momentarily interrupted; while, alternatively, this same circuitis connected to be supplied by the storage battery 45 in the instancewhere the primary power is interrupted for an extended period. To thisend, the relay 28 has a contact arm 86 which, when in its normallyclosed condition, completes a circuit with a tap 87 on the secondarywinding 55 of the transformer 47. A second contact arm 88 of the relay28 couples the dropping impedance 49 of the battery charging circuit tothe storage battery 45 when the relay is energized. A second relay 90has a pair of contact arms 91, 92 and an energization coil 93 connectedbetween one side of the secondary winding 55 of the transformer 47 andthe takeofi tap 87 of the same winding 55. The contact arms 91, 92 havenormally open and normally closed positions for respectively connectingthe emergency lamp to the primary power source (via the relay 28 and thetransformer 47) or to the storage battery 45 (via the thermal timeswitch 79). The takeoff tap 87 of the secondary winding 55 provides thenecessary AC voltage for driving the. emergency lamp 40 and the relaycoil 93. In the present instance, both the lamp 40 and coil 93 areoperative at 12 volts AC, and the storage battery 45 has a fully chargedvoltage of 12 volts DC.

To facilitate an understanding of the operation, assume first that theswitch 22 becomes closed to supply the ballast circuit 15 with power viathe power lines 20, 21. If the electrical discharge lamps 10, I 1 havecooled to room temperature from any previous operation, the ballastcircuit 15 will provide a starting voltage sufficiently high to strikethe arc and illuminate the lamps 10, 11. Current begins to flow throughthe primary lighting circuit, energizing the coil 27 of the relay 28 andheating up the resistor 29. The contact arms 86, 88 of the relay 28 moveto their normally open positions, as shown in FIG. 1. If the battery 45is not already charged to its fully charged state, the pressure switch75 will be closed, and the charging circuit will charge the battery viathe transformer 47, the bridge rectifier 48 and dropping impedance 49.When the battery 45 becomes fully charged, the pressure switch 75 opens.Meanwhile, the heating resistor 29 has reached a temperature sufficientto close the thermal time switch 79. The energization coil 93 of therelay 90 has been energized by virtue of its connection to the secondaryof the transformer 47, and the contact arms 91, 92 have moved to theirnormally open positions.

If a momentary fluctuation now occurs in the primary source voltage, thelamps 10, 11 will be extinguished. If the lamps have reached theiroperating temperature, the ballast circuit 15 will be unable to providea high enough voltage to restrike the arc. Even though the primary powersource is immediately reactivated, the current through the lamp circuitis effectively zero. The relay 28 becomes deenergized, with the contactarms 86, 88 assuming their normally closed positions. Since primarypower was immediately reestablished, the relay 90 remains energized toconnect the emergency lamp 40 to the primary power source via thetransformer 47 and the contact arm 86 of the relay 28. Although theemergency lamp 40 is providing illumination, there is no load put on thebattery 45. When the electrical discharge lamps 10, 11 coolsufficiently, their arcs will be again struck by the ballast circuit 15,and current will flow in the primary lighting circuit. The relay 28 willbecome energized, disconnecting the emergency lamp 40 from the primarypower source.

If, instead of a momentary power interruption, there had been apermanent power stoppage, such as when the main switch 22 is opened, adifferent sequence of events would take place. The lamps 10, 11 wouldagain be extinguished and the relay 28 would be deenergized. Sinceprimary voltage is no longer supplied to the transformer 47, the relay90 would also be deenergized, connecting the emergency lamp 40 acrossthe storage battery 45 via the thermal time switch 79. The emergencylamp 40 would glow to illuminate the area until the heating resistor 29,which is now deprived of current, cools sufficiently to open the thermaltime switch 79. After 10 to 15 minutes, the switch 79 opens and theemergency lamp 40 goes off. If the switch 22 is closed at any timeduring the time delay period of the switch 79, the relay 90 will beenergized to disconnect the lamp 40 from the battery 45. Depending uponwhether the discharge lamps 10, 11 have cooled sufficiently to allowignition by the ballast circuit 15, the illumination for the area willthen be supplied by the discharge lamps 10, 11 or the emergency lamp 40(via the primary power source instead of the battery 45).

If the above-described circuit is part of a lighting system which isused every evening, it is seen that the emergency lamp 40 will beoperative for a period of time after the primary lighting circuit isturned off in the morning; the storage battery 45 will partiallydischarge every morning and will be recharged every evening when theprimary power is turned on. Such a discharge-charge cycle extends thelife of the battery.

An alternative embodiment of the present invention is shown in FIG. 2.This embodiment is similar in several ways to that shown in FIG. 1;consequently, the reference numbers for the elements of FIG. 1 arecarried over to those elements of FIG. 2 which provide an identicalfunction, with the addition of subscripts. All of the alternativefeatures shown in FIG. 2 are applicable to the preferred embodimentshown in FIG. I; therefore, all modifications to either circuitincorporating features of the other are within the scope of the presentinvention.

Turning then to FIG. 2, there is shown an electrical discharge lamp 10aconnected for energization by a ballast circuit 15a. The ballast circuitprimary winding 17a is coupled to a primary source of power on the lines20a and 210. It will be noted that the lamp a is connected directlyacross the secondary winding 18a of the ballast circuit a, forming anintegrated unit for connection to the AC power lines.

A secondary or emergency power source is provided by a battery 45a, thecharge of which is maintained by a batterycharging circuit in a mannersimilar but not identical to that described for the preferredembodiment. in this case, the battery-charging circuit is selectivelycontrolled to provide a fast charge or a trickle charge to the battery45a, the rate of charge depending upon the voltage existing across thebattery. To this end, the battery-charging circuit includes atransformer. 47a connected to the primary power source via lines 52a,53a. The transformer output is fed to a bridge rectifier 48a, whichprovides full-wave rectification at the terminals 65a and 66a. Acharging current is selectively applied to the battery 45a through alow-impedance path consisting of a fixed resistor 49a and a variableresistance 49b or through a high-impedance path consisting of a fixedresistor 49c and a variable resistor 49d. For sensing the voltage acrossthe battery 45a there is provided a relay 100 having an energizationcoil 101 and a contact arm 102, the coil 101 being in series with avariable resistor 104 connected across the battery 45a. The resistance104 is preset so that the coil 101 is energized as the storage battery45a reaches its full operating voltage. Energization of the coil 101trips the contact arm 102, switching the output terminal 66a of thebridge 48 from the low-impedance path (resistors 49a, 49b) to thehigh-impedance path (resistors 49c, 49d). In this way a switch from afast charge rate to a slow charge rate is accomplished, protecting thestorage battery 45a from overcharging.

A secondary lighting circuit including a lamp 40a is disposed forconnection across the storage battery 45a in a manner hereinafterdescribed.

For responding to the interruption of illumination of the primarylighting source there is provided a light-sensing circuit having its ownDC power supply 110, a photosensitive device 111 and a relay 112. Thephotosensitive device 111 in this case is a photoresistor of the typehaving-a very high resistance value in darkness and a very lowresistance value in the presence of light. The DC power supply for thesensing circuit includes a bridge rectifier 115 consisting of fourdiodes 116-1 19 connected across the primary source of power on thelines a and 21a. A pair of output terminals 120, 121 of the bridge '115supply a full-wave rectified AC signal across a capacitor 123, thecapacitor 123 serving to reduce the ripple component of the signal. In aseries loop with the power supply 1 10 is a variable control resistance125, the photosensitive device 111 and the energization coil 127 of therelay 112. The relay 112 has a normally closed contact arm 128connecting one terminal 410 of the lamp 40a to one side of the storagebattery 45a.

in operation, the relay 112 will not become energized until the currentflowing through the coil 127 becomes sufficiently high. This current isdetermined by the variable resistance 125 and the photoresistor 111.While the arc is ignited in the lamp 10a, the resistance of the photodevice 111 is sufficiently low to allow a high current to flow throughthe sensing circuit, causing the relay 112 to be energized,disconnecting the lamp 40a from the storage battery 45a. As describedpreviously, a momentary interruption in the primary power source willcause the lamp 10a to be extinguished until it cools sufficiently to berestarted by the ballast circuit 15a. During this period of darkness theresistance of the photo device 111 becomes extremely high, decreasingthe current through and deenergizing the relay 112. The contact arm 128assumes its normally closed position, connecting the terminal 41a of thelamp 40a to the storage battery 45a, enabling the secondary lightingcircuit to provide emergency illumination. The relay 112 will remaindeenergized until the arc is again struck in the discharge lamp 143a.

In accordance with another feature of the present invention, means areprovided for disabling the secondary lighting circuit when the primarypower source has been interrupted or disconnected for a prolonged periodof time. This is desirable to prevent the lamp 40a from completelydischarging the storage battery 45a when the primary power is notavailable to recharge the battery. in the previous embodiment thethermal switch 79 provided this feature, whereas in the presentembodiment a time delay relay 141 is provided, having its coil 142connected across the primary power lines 20a, 21a. The device 141 has anormally open contact arm 143 in series with the lamp 400 of thesecondary lighting circuit. While the primary power source is operative,the relay 141 is energized, so that the illumination sensing circuitoperates in the manner described above, causing the lamp 400 to beilluminated when the discharge lamp 10a is extinguished. A time delayrelay may be chosen which has a delay time of 10 minutes. Assuming thisdelay, it is seen that the secondary lighting circuit will be disabledfrom the battery 45a in 10 minutes after the primary power becomesinoperative. if the interruption of primary power is only momentary, orless than 10 minutes, the coil 142 of the relay 141 will be reenergizedbefore the contact arm 143 opens, and the lamp 400 will providecontinuous illumination until the discharge lamp is reactivated. It willbe noted, therefore, that the lamp 40a will provide illumination for 10minutes after the lighting system is turned off in the morning insimilar fashion to the operation of the preferred embodiment of FIG. 1.The battery 4511 will experience the same advantageous charge-dischargedaily cycling described above for the previous embodiment.

From the above description it will be evident that there has beenbrought to the art a novel emergency lighting system for use withmercury vapor lamps or the like which is efficient and virtuallymaintenance-free and which may be used with a variety of differentlighting systems with only minor modifications.

I claim as my invention:

1. A lighting circuit, comprising,

a. input lines providing a primary source of power;

b. a primary lighting circuit including electrical discharge lamp meanshaving different energy demands during hot starting, cold starting andnormal operating periods;

c. a storage battery;

d. charging means coupled to said input lines and adapted to beselectively coupled to charge said battery;

e. charge control means responsive to the substantially chargedcondition of said battery to prevent overcharge thereof by said chargingmeans;

f. sensing means responsive to an interruption in the operation of saidprimary lighting circuit;

g. a secondary lighting circuit;

h. switching means actuated by said sensing means to connect saidbattery for energizing said secondary lighting circuit;

i. and a time delay device for disconnecting said battery from saidsecondary lighting circuit a predetermined time interval subsequent toits. connection thereto, thereby preventing the complete discharge ofsaid battery.

2. A lighting system comprising, in combination,

a. input lines providing a primary source of power;

b. a primary lighting circuit including electrical discharge lamp meanshaving different energy demands during hot starting, cold starting andnormal operating periods and ballast means for supplying energy for saidlamp means during cold starting and normal operating periods;

0. a secondary power source;

d. a secondary lighting circuit;

e. switching means coupled to said secondary lighting circuit andresponsive: el. to a momentary interruption of current in said primarylighting circuit to energize said secondary lighting circuit from saidprimary power source, and

e2. to an extended period of current interruption in said primarylighting circuit to energize said secondary lighting circuit from saidsecondary power source.

3. A lighting system according to claim 2 wherein said secondary powersource is a battery and wherein said combination further f.battery-charging means supplied by said primary power source and adaptedto charge said battery during normal operation of said primary lightingcircuit.

4. A lighting system according to claim 3 further including g. chargecontrol means responsive to the substantially charged condition of saidbattery to prevent overcharging thereof,

h. and discharge control means operative to disconnect said battery fromsaid secondary lighting circuit a predetermined time interval afterenergization of said secondary lighting circuit from said battery,whereby complete discharge of said battery is prevented.

5. A lighting circuit according to claim 4 wherein said dischargecontrol means comprises a heating resistor in circuit with said primarylighting circuit and a thermal switch connected in series with saidbattery, said switch being operative to close when current flows throughsaid primary lighting circuit to heat said resistor and to open afterthe heating resistor has cooled due to a loss of current in said primarylighting circuit, the cooling time defining a discharge interval forsaid battery.

6. A lighting system comprising, in combination,

a. input lines providing a primary source of power;

b. a primary electric gaseous discharge device of a type whose startingpotential at normal operating temperature is far in excess of itsstarting potential at room temperature;

. a ballast circuit capable of generating a potential sufficient forstarting said device at room temperature and for sustaining normaloperation thereof;

. a secondary power source;

. a secondary lighting circuit;

a light-sensing circuit supplied by said input lines and opticallycoupled to said discharge device for providing an electrical response tothe inoperative condition thereof; and

g. switching means controlled by said light-sensing circuit to energizesaid secondary lighting circuit from said secondary power source uponoccurrence of said electrical response.

7. A lighting system according to claim 6 wherein said secondary powersource is a battery and wherein said combination further comprises,

h. a battery-charging circuit supplied by said primary power source andselectively operable to provide both a fast charge and a trickle charge,depending upon the charge condition of said battery.

8. A lighting system according to claim 7 further including dischargecontrol means operative to disconnect said secondary lighting circuitfrom said battery an interval of time subsequent to an interruption ofsaid primary power source, thereby preventing excessive discharge ofsaid battery.

. A lighting system comprising,

a. a primary lighting circuit including electrical discharge lamp meanshaving different energy demands during hot starting, cold starting, andnormal operating periods and ballast means for supplying said differentenergy demands during cold starting and normal operating periods;

b. a secondary power source;

. a secondary lighting circuit;

. sensing means responsive to an interruption in the operation of saidprimary lighting circuit;

. switching means selectively interposed in series with said secondarylighting circuit and adopted for actuation by said sensing means tocouple said secondary power source to said secondary lighting circuit,energizing said secondary lighting circuit to provide an auxiliarysource of illumination;

f. charge control means associated with said secondary power source; and

g. discharge control means including a time delay device automaticallyoperable in response to the inoperative condition of said primarylighting circuit, said charge and discharge control means beingoperative to allow cyclical charging and discharging of said secondarypower source in controlled amounts in accordance with the normal dailyON-OF F cycle of said primary lighting circuit.

10. In an auxiliary lighting system for use with a primarynight-lighting system an auxiliary power supply including,

a. a storage battery,

b. a charging circuit for selectively charging said battery,

c. means controlling the charge rate to said battery in accordance withthe charge state of said battery, and

d. time delay means automatically rendered operative duringinoperativeness of said primary night-lighting system for controllingthe discharge period of said battery, said charge' and discharge controlmeans being cyclically operable in conjunction with the normal dailyON-OFF cycle of said primary night-lighting system and said charge anddischarge of said battery being controlled in predetermined amounts soas to prolong the operating life of said battery.

1 1. A lighting system comprising,

a. input lines providing a primary source of power,

b. a primary electric gaseous discharge device whose starting potentialat its normal operating temperature is far in excess of the startingpotential required at room temperature,

. a ballast circuit capable of supplying a sufficient starting potentialwhen said device is at room temperature,

a storage battery,

. a battery-charging circuit supplied by said primary power source andoperable to provide a fast charging current and a trickle chargingcurrent,

f. switching means selectively coupling said fast charge current or saidtrickle charge current to said battery in accordance with the chargestate of said battery,

g. a light-sensing circuit including a direct current power supply and aphotosensitive device optically coupled to said discharge device toprovide an electrical response to an interruption of illuminationthereof;

h. a secondary lighting circuit;

. switching means associated with said sensing circuit for energizingsaid secondary lighting circuit from said battery upon the occurrence ofsaid electrical response; and

j. a time delay relay having a pair of contacts in circuit with saidsecondary lighting circuit and an energization coil adapted forenergization by said primary power source, said contacts being operativeto open a predetermined interval after an interruption in said primarysource of power so that complete discharge of said battery does notoccur.

12. In an emergency lighting circuit for use with electrical gaseousdischarge lighting systems having a ballast circuit capable of providinga potential sufficient to start gaseous discharge lamps at roomtemperature but insufficient to start the lamps at their normaloperating temperature, the combination comprising,

a. input lines providing a primary source of power for said ballastcircuit;

b. a secondary power source;

c. a secondary lighting circuit, and

d. switching means coupled to said secondary lighting circuit andresponsive:

d1. to a momentary interruption of current through said gaseousdischarge lamps to energize said secondary lighting circuit from saidprimary power source, and

d2. to an extended period of current interruption in said lamps toenergize said secondary lighting circuit from said secondary powersource.

g. discharge control means operative to disconnect said battery fromsaid secondary lighting circuit a predetermined time interval afterenergization of said secondary lighting circuit from said battery,whereby complete discharge of said battery is prevented.

1. A lighting circuit, comprising, a. input lines providing a primarysource of power; b. a primary lighting circuit including electricaldischarge lamp means having different energy demands during hotstarting, cold starting and normal operating periods; c. a storagebattery; d. charging means coupled to said input lines and adapted to beselectively coupled to charge said battery; e. charge control meansresponsive to the substantially charged condition of said battery toprevent overcharge thereof by said charging means; f. sensing meansresponsive to an interruption in the operation of said primary lightingcircuit; g. a secondary lighting circuit; h. switching means actuated bysaid sensing means to connect said battery for energizing said secondarylighting circuit; i. and a time delay device for disconnecting saidbattery from said secondary lighting circuit a predetermined timeinterval subsequent to its connection thereto, thereby preventing thecomplete discharge of said battery.
 2. A lighting system comprising, incombination, a. input lines providing a primary source of power; b. aprimary lighting circuit including electrical discharge lamp meanshaving different energy demands during hot starting, cold starting andnormal operating periods and ballast means for supplying energy for saidlamp means during cold starting and normal operating periods; c. asecondary power source; d. a secondary lighting circuit; e. switchingmeans coupled to said secondary lighting circuit and responsive: e1. toa momentary interruption of current in said primary lighting circuit toenergize said secondary lighting circuit from said primary power source,and e2. to an extended period of current interruption in said primarylighting circuit to energize said secondary lighting circuit from saidsecondary power source.
 3. A lighting system according to claim 2wherein said secondary power source is a battery and wherein saidcombination further f. battery-charging means supplied by said primarypower source and adapted to charge said battery during normal operationof said primary lighting circuit.
 4. A lighting system according toclaim 3 further including g. charge control means responsive to thesubstantially charged condition of said battery to prevent overchargingthereof, h. and discharge control means operative to disconnect saidbattery from said secondary lighting circuit a predetermined timeinterval after energization of said secondary lighting circuit from saidbattery, wheReby complete discharge of said battery is prevented.
 5. Alighting circuit according to claim 4 wherein said discharge controlmeans comprises a heating resistor in circuit with said primary lightingcircuit and a thermal switch connected in series with said battery, saidswitch being operative to close when current flows through said primarylighting circuit to heat said resistor and to open after the heatingresistor has cooled due to a loss of current in said primary lightingcircuit, the cooling time defining a discharge interval for saidbattery.
 6. A lighting system comprising, in combination, a. input linesproviding a primary source of power; b. a primary electric gaseousdischarge device of a type whose starting potential at normal operatingtemperature is far in excess of its starting potential at roomtemperature; c. a ballast circuit capable of generating a potentialsufficient for starting said device at room temperature and forsustaining normal operation thereof; d. a secondary power source; e. asecondary lighting circuit; f. a light-sensing circuit supplied by saidinput lines and optically coupled to said discharge device for providingan electrical response to the inoperative condition thereof; and g.switching means controlled by said light-sensing circuit to energizesaid secondary lighting circuit from said secondary power source uponoccurrence of said electrical response.
 7. A lighting system accordingto claim 6 wherein said secondary power source is a battery and whereinsaid combination further comprises, h. a battery-charging circuitsupplied by said primary power source and selectively operable toprovide both a fast charge and a trickle charge, depending upon thecharge condition of said battery.
 8. A lighting system according toclaim 7 further including i. discharge control means operative todisconnect said secondary lighting circuit from said battery an intervalof time subsequent to an interruption of said primary power source,thereby preventing excessive discharge of said battery.
 9. A lightingsystem comprising, a. a primary lighting circuit including electricaldischarge lamp means having different energy demands during hotstarting, cold starting, and normal operating periods and ballast meansfor supplying said different energy demands during cold starting andnormal operating periods; b. a secondary power source; c. a secondarylighting circuit; d. sensing means responsive to an interruption in theoperation of said primary lighting circuit; e. switching meansselectively interposed in series with said secondary lighting circuitand adopted for actuation by said sensing means to couple said secondarypower source to said secondary lighting circuit, energizing saidsecondary lighting circuit to provide an auxiliary source ofillumination; f. charge control means associated with said secondarypower source; and g. discharge control means including a time delaydevice automatically operable in response to the inoperative conditionof said primary lighting circuit, said charge and discharge controlmeans being operative to allow cyclical charging and discharging of saidsecondary power source in controlled amounts in accordance with thenormal daily ON-OFF cycle of said primary lighting circuit.
 10. In anauxiliary lighting system for use with a primary night-lighting systeman auxiliary power supply including, a. a storage battery, b. a chargingcircuit for selectively charging said battery, c. means controlling thecharge rate to said battery in accordance with the charge state of saidbattery, and d. time delay means automatically rendered operative duringinoperativeness of said primary night-lighting system for controllingthe discharge period of said battery, said charge and discharge controlmeans being cyclically operable in conjunction with the normal dailyON-OFF cycle of said primary night-lighting system And said charge anddischarge of said battery being controlled in predetermined amounts soas to prolong the operating life of said battery.
 11. A lighting systemcomprising, a. input lines providing a primary source of power, b. aprimary electric gaseous discharge device whose starting potential atits normal operating temperature is far in excess of the startingpotential required at room temperature, c. a ballast circuit capable ofsupplying a sufficient starting potential when said device is at roomtemperature, d. a storage battery, e. a battery-charging circuitsupplied by said primary power source and operable to provide a fastcharging current and a trickle charging current, f. switching meansselectively coupling said fast charge current or said trickle chargecurrent to said battery in accordance with the charge state of saidbattery, g. a light-sensing circuit including a direct current powersupply and a photosensitive device optically coupled to said dischargedevice to provide an electrical response to an interruption ofillumination thereof; h. a secondary lighting circuit; i. switchingmeans associated with said sensing circuit for energizing said secondarylighting circuit from said battery upon the occurrence of saidelectrical response; and j. a time delay relay having a pair of contactsin circuit with said secondary lighting circuit and an energization coiladapted for energization by said primary power source, said contactsbeing operative to open a predetermined interval after an interruptionin said primary source of power so that complete discharge of saidbattery does not occur.
 12. In an emergency lighting circuit for usewith electrical gaseous discharge lighting systems having a ballastcircuit capable of providing a potential sufficient to start gaseousdischarge lamps at room temperature but insufficient to start the lampsat their normal operating temperature, the combination comprising, a.input lines providing a primary source of power for said ballastcircuit; b. a secondary power source; c. a secondary lighting circuit,and d. switching means coupled to said secondary lighting circuit andresponsive: d1. to a momentary interruption of current through saidgaseous discharge lamps to energize said secondary lighting circuit fromsaid primary power source, and d2. to an extended period of currentinterruption in said lamps to energize said secondary lighting circuitfrom said secondary power source.
 13. The combination in an emergencylighting system according to claim 12 wherein said secondary powersource is a battery and wherein said combination further includes; e. abattery-charging circuit, f. charge control means responsive to thesubstantially charged condition of said battery to prevent overchargingthereof, and g. discharge control means operative to disconnect saidbattery from said secondary lighting circuit a predetermined timeinterval after energization of said secondary lighting circuit from saidbattery, whereby complete discharge of said battery is prevented.